Copy / paste not working - breaks text formatting and usually drops any vector content as well. This happens whether the copy/paste is within one Illustrator file or between two. VERY frustrating. I've found that I can occasionally get it to work by copying and pasting within the same document (everything must be grouped as one), and if it is successful, quickly copy the pasted version and then it might paste into the other Illustrator file.

Solution from support was to downgrade from 24.4 to 24.01. This seems to have done the trick - but now I can't allow CC to update Illustrator.